Technical Support Document - Supplemental 

This Technical Support Document (TSD) evaluates Colorado’s impact to visibility in nearby outand organic carbon. The Western Regional Air Pevaluation of state source attribution: (1) PM Source Apportionment Technology (PSAT) modeling and Potential (WEP). These analysis tools were applied to the Class I areas that are indicated by a yellow dot in TSD, the PSAT and WEP analysis tools, along with a review of approach (WOE) to determine whether emissions from reasonable progress goals (RPG) under the Regional Haze program. 

Figure 1. Nearby Class I Areas Evaluated with PSAT and WEP

The WRAP analyses show that Canyonlands National Park is the Class I area where visibColorado. Therefore, the WOE information provided in this TSD focuses primarily on Canyonlands with the kother nearby Class I areas will be less. The PSAT and WEP analysis tools are summar

Supplemental Weight-of-Evidence (WOE) 

the 110 Transport SIP 

evaluates Colorado’s impact to visibility in nearby out-of-state Class 

Partnership (WRAP) has produced the following two analysis 

PM Source Apportionment Technology (PSAT) modeling and (2) 

These analysis tools were applied to the Class I areas that are indicated by a yellow dot in 

is tools, along with a review of current and future year inventories, are used 

emissions from Colorado sources interfere with the ability of nearby S

reasonable progress goals (RPG) under the Regional Haze program. 

Figure 1. Nearby Class I Areas Evaluated with PSAT and WEP

The WRAP analyses show that Canyonlands National Park is the Class I area where visibility is most impacteColorado. Therefore, the WOE information provided in this TSD focuses primarily on Canyonlands with the k

The PSAT and WEP analysis tools are summarized below. 

Evidence (WOE) An

state Class 

analysis 

(2) We

These analysis tools were applied to the Class I areas that are indicated by a yellow dot in 

current and future year inventories, are used 

ability of nearby S

ility is most impacte

Colorado. Therefore, the WOE information provided in this TSD focuses primarily on Canyonlands with the k
 (1) PSAT: The Regional Modeling Center (RMC) at the University of California – Riverside developed the PSAT algorithAir quality Model with extensions (CAMx) model to assess source attribution. The PSAT analysis is used to a

particularly sulfate and nitrate from a specific location within the WRAP modeling domain. The PSAT algorith

ammonia chemistry to a system of tracers or “tags” to track the chemical transformations, transport and remostate or region (i.e. Mexico, Canada) is assigned a unique number that is used to tag the emissions from eac

within the WRAP modeling domain. Due to time and computational limitations, only point, mobile, area and fThe PSAT algorithm was also used, in a limited application (e.g. no state or regional attribution), to track natuspecies of organic aerosols at each Class I area. The organic aerosol tracer tracked both primary and secon

(POA & SOA). In 2007, the WRAP RMC performed two modeling runs using the 2002 planning inventory (pla

case inventory (base18b) for which PSAT analysis was completed. In the spring of 2009, the WRAP released 

planning inventory (plan02d) and the 2018 preliminary reasonable progress inventory (prp18b), but unfortuna

done due to insufficient funding. It is important to note that the PSAT results used in this analysis are derived 

inventory and not the subsequent prp18b inventory. 

(2) WEP: The Weighted Emissions Potential analysis (WEP) was developed as a screening tool for states to decide wh

the potential to contribute to haze formation at specific Class I areas, based on both the 2002 and 2018 emis

method does not produce highly accurate results because, unlike the air quality model and associated PSAT 

account for chemistry and removal processes. Instead, it relies on an integration of gridded emissions data, b

time data, a one-over-distance factor to approximate deposition, and a normalization of the final results. Res

is indicative of general flow patterns, but does not necessarily imply the area contributed significantly to haze 

Therefore, users are cautioned to view the WEP as one piece of a larger, more comprehensive weight of evid

unlike the PSAT analysis, the WEP results were produced for the PRP 2018b emission inventory upon which 

PSAT Evaluation of Colorado Impacts on nearby Class I areas:

For each Class I area over the planning period, the Regional Haze rule requires States to ensure no degrada

days (best days) and provide for improvement in visibility for the most impaired days (worst days). The State 

that provide for reasonable progress towards achieving natural visibility conditions. Consequently, the impac2018 worst days are evaluated to see if further improvement can be achieved. While the Regional Haze rule ensure no degradation of visibility on the best days, the WRAP modeling projects that visibility on the best da

at any of the surrounding Class I areas. For example, modeling indicates that the visibility at Canyonlands N

days is expected to improve from 3.8 dv to 3.5 dv. Therefore, this TSD focuses on analysis of the worst days
Table 1 shows Colorado’s contribution to sulfate and nitrate extinction on the worst days at nearby Class I arebase18b modeling scenarios. In 2002, the largest contributions from Colorado, 3.4% for sulfate and 6.9% for Canyonlands. 

Table 1: Colorado Sulfate and Nitrate Impacts on Nearby Class I areas 

The emission inventories associated with PSAT and WEP were developed by the WRAP (primarily under con

Research Group) based on on-the-books (OTB) and on-the-way (OTW) emission control assumptions. For pTransport SIP, only federally enforceable controls may be considered in determining a State’s impact on a ne

Consequently, some of the Colorado OTB and OTW emissions reductions that were included in the 2018 basfederally enforceable and must be added back into the emission projections to ensure the most conservative 

state Class I area is determined. Table 2 provides a summary of the emission reductions (Submitted to EPA been added back into the emission inventory for purposes of determining visibility impacts. Since anticipated 

at sources such as Drake and Pawnee were not included in the emission inventory for Base 2018b, there wa

back when rescaling the PSAT results. The same is true for NOx emission reductions at the CEMEX Lyons c
Table 2: Summary of Control Program Emission Reductions and Enforceability - from 11

In light of the fact that the WRAP RMC is now disbanded, there is no ability to perform another PSAT run refle

emission controls that are not federally enforceable that should be added back into the emission inventory. Cscaling method was developed as a means for ascertaining changes to visibility impacts at a particular Class 

provide an example demonstration of the visibility changes at Canyonlands for sulfate and nitrate that are est

increases to Colorado’s emissions due to lack of federal enforceability. 

Measure Pollutant SIP Approved [tons/year]

SO2 NOx VOC SO2 

Craig & Hayden Controls SO2 18,000

O&G Tank Controls in Front Range by 2007 VOC 52,000Mobile Source Fleet Turnover by 2020 NOx & VOC 55,000O&G RICE Controls - EAC by 2005 NOx & VOC 8,300Drake Controls SO2 6,200Pawnee Controls SO2 9,000Cemex Controls NOx 1,200Metro VERA SO2 24,000Comanche Controls SO2 6,500Additional O&G Tank Controls in FR by 2010 VOC 18,000Mobile Source I/M Program & Fuels NOx & VOC 4,000 4,000O&G Pnuematic Controls - Statewide VOC O&G Tank Controls - Statewide VOC O&G RICE Controls - Statewide by 2010 NOx & VOC Araphaoe & Cameo Shutdown SO2 & NOx 

5,30

Totals: 133,300 45,700 5,200 22,000 5,300 

Combined Totals:

Total SO2 - Not Federally Enforceable : 30,500 tpy

Total NOx - Not Federally Enforceable : 4,000 tpy

Total VOC - Not Federally Enforceable : 4,000 tpy

Note: It is assumed that recent mobile I/M and fuels program are not fedeadded back in Base 18.Note: Cemex SNCR NOx reductions not in Base 2018b EI, O&G RICE adopted 

2018b (May 2007), thus not in EI, not sure about Mobile NOx reductions, thuNote: O&G Tank Controls, O&G Pnuematic Controls, O&G Statewide RICE & 

develp of Base 2018b (May 2007), thus not in EI.Note: Drake,Pawnee, Arapahoe & Cameo SO2 reductions not in Base 2018b 

Summary of Control Program Emission Reductions for NOx, SO2 and VOC

Submitted to EPA [tons/year] 
Figure 2: Canyonlands 2018 Worst Days – Rescaled 2018 Sulfate Model Projectio

As indicated in the Figure 2 above, SO2 emissions were increased by 30,500 tons per year (see red box) bec

not federally enforceable (e.g. either submitted to EPA and not yet acted upon or State-only). The resultant r

model projection is 5.175 Mm-1 (see red arrow), which is about 0.87% higher than the original PSAT model pminimal sulfate impact from Colorado sources (originally 2.30% and increased to 3.17%), it is not surprising tchange is so small. 

Canyonlands National Park

Emissions Potential Analysis

Sulfate Baseline 

Extinction Source Region

Original 

Overall PSAT 

Impact

Rescaled 

Overall PSAT 

Impact

Change in 

PSAT Impact Source Category PSAT Category Contribution Sub Category Sub Category Contribution Sub Category Emissions Emissions that are not federally enforceable 

Other WRAP States 39.08% 39.08% 0.00% All Sources 

Outside Domain* 35.47% 35.47% 0.00% GeosChem 

CEN & EUS 3.12% 3.12% 0.00% All Sources 

CAN, MEX & PO 20.03% 20.03% 0.00% All Sources 

Colorado 2.30% 3.17% 0.87% All Sources 

100.00% 100.87%

Point 85.7% 

External Combustion Boilers 89.4% 61,854 30,500 

Sulfate Extinction Industrial Processes 8.6% 5,978 - 

[Mm-1] - 

Baseline bSO4: 5.580 30,500

2018 URP bSO4: 4.240 Area 7.1% 

Model Projection: 5.130 Stationary Source Fuel Combustion 98.8% 7,490 - 

Rescaled Model Projection: 5.175 

- % Change in Model Projection: 0.87% 

-- Mobile 7.1% 

On-Road Mobile 60.5% 568 - 

Off-Road Mobile 39.5% 371 - 

 

-- Nat. Fires & Bio. 0.0% 

Natural Fire 100.0% 2,542 - 

 

- -- All Sources 100.0% Total Increase: 30,500 

Notes:

SO2 [tons/year]

24.6%

See Emissions Reductions Spreadsheet for SO2 emissions that are not federally enforceable.

* Aproximately 35% of Sulfate is from outside model domain (mostly global 

transport)
Figure 3: Canyonlands 2018 Worst Days – Rescaled 2018 Nitrate Model Projectio

Similarly, as indicated in Figure 3 above, NOx emissions were increased by 4,000 tons per year (see red box

are not federally enforceable, (e.g. either submitted to EPA and not yet acted upon or state-only). The resulta

model projection is 3.053 Mm-1 (see red arrow), which is about 0.09% higher than the original PSAT model pminor nitrate impact from Colorado sources (originally 6.88% and increased to 6.97%) and the small increase 

not surprising that the nitrate extinction change is so small. Unfortunately, the organic carbon (OC) PSAT modeling was limited to tracking three categories of OC (primasecondary biogenic, and secondary anthropogenic) but no state or regional attribution was included. Conseq

Canyonlands National Park

Emissions Potential Analysis

Nitrate Baseline 

Extinction Source Region

Overall PSAT 

Impact

Rescaled 

Overall PSAT 

Impact

Change in 

PSAT Impact Source Category PSAT Category Contribution Sub Category Sub Category Contribution Sub Category Emissions Emissions that are not federally enforceable 

Other WRAP States 68.13% 68.13% 0.00% All Sources 

Outside Domain* 22.50% 22.50% 0.00% GeosChem 

CEN & EUS 0.00% 0.00% 0.00% All Sources 

CAN, MEX & PO 2.50% 2.50% 0.00% All Sources 

Colorado 6.88% 6.97% 0.09% All Sources 

100.00% 100.09%

Point 27.3% 

External Combustion Boilers 71.3% 79,982 - 

Nitrate Extinction Internal Combustion Engines 19.3% 21,705 - 

[Mm-1] Industrial Processes 9.0% 10,106 - 

Baseline bSO4: 2.970 - 2018 URP bSO4: 2.430 Area 45.5% 

Model Projection: 3.050 Industrial Processes 61.9% 27,709 - 

Rescaled Model Projection: 3.053 Stationary Source Fuel Combustion 36.5% 16,321 - 

% Change in Model Projection: 0.09% 

-- Mobile 18.2% 

On-Road Mobile 52.6% 45,249 4,000 

Off-Road Mobile 47.4% 40,804 - 

 

- 4,000

Nat. Fires & Bio. 9.1% 

Natural Fire 19.9% 9,297 - 

Biogenic 80.1% 37,349 - 

 

-- All Sources 100.0% Total Increase: 4,000 

Notes:See Emissions Reductions Spreadsheet for NOx emissions that are not federally enforceable.

13.1%

NOx [tons/year]

* Aproximately 23% of Nitrate is from outside model domain (mostly global transport)
determine Colorado OC impacts at Canyonlands or any changes in visibility associated with changes to VOC 

important to note that anthropogenic SOA represents a very small portion of total particulate OC at Ca

n

4. Therefore, VOC emissions (form secondary organic aerosol) are a very small contributor to total particulat

Figure 4: Canyonlands Organic Aerosol PSAT modeling for 2018 Worst Days

In summary the rescaled PSAT model projections and nitrate (0.09%). Converting these rescaled extinction values to a deciview metricdifficult without the original PSAT model input and output files since the conversion to deciviews involves a loMoreover, and as noted earlier, the PSAT predictions represent impacts in the 2018 base case and not the 2case. However, it is possible to approximate the change in the reasonablerecalculate the baseline haze index (2000-2004) using daily 20% worse case monitored species2) recalculate 2018 predicted reasonable progress goal haze index by applying Class I Area specific annual r(RRFs) provided by WRAP to the daily 20% worst case monitored for each pollutant; 3) assume thatnitrates and sulfates identified by WRAP tracer modeling for the 2018 base case is same for the 2018 reason4) rescale sulfate extinction and nitrate extinction in step 2recalculate the reasonable progress goals that would be expected.

determine Colorado OC impacts at Canyonlands or any changes in visibility associated with changes to VOC important to note that anthropogenic SOA represents a very small portion of total particulate OC at Ca

nyonla

4. Therefore, VOC emissions (form secondary organic aerosol) are a very small contributor to total particulat

Figure 4: Canyonlands Organic Aerosol PSAT modeling for 2018 Worst Days

del projections for the 2018 base case indicate very small increases in ext

deciview metric, as used to establish reasonable progress g

difficult without the original PSAT model input and output files since the conversion to deciviews involves a lo

as noted earlier, the PSAT predictions represent impacts in the 2018 base case and not the 2

it is possible to approximate the change in the reasonable progress goal by using the followi

2004) using daily 20% worse case monitored species extinction fro

recalculate 2018 predicted reasonable progress goal haze index by applying Class I Area specific annual r

(RRFs) provided by WRAP to the daily 20% worst case monitored for each pollutant; 3) assume that Colorad

by WRAP tracer modeling for the 2018 base case is same for the 2018 reason

and nitrate extinction in step 2 to account for Colorado emissions that are not fed

recalculate the reasonable progress goals that would be expected. Note that in approximating the change in determine Colorado OC impacts at Canyonlands or any changes in visibility associated with changes to VOC 

yonla

4. Therefore, VOC emissions (form secondary organic aerosol) are a very small contributor to total particulat

Figure 4: Canyonlands Organic Aerosol PSAT modeling for 2018 Worst Days

indicate very small increases in ext

, as used to establish reasonable progress g

difficult without the original PSAT model input and output files since the conversion to deciviews involves a lo

as noted earlier, the PSAT predictions represent impacts in the 2018 base case and not the 2

by using the followi

extinction fro

recalculate 2018 predicted reasonable progress goal haze index by applying Class I Area specific annual r

Colorad

by WRAP tracer modeling for the 2018 base case is same for the 2018 reason

to account for Colorado emissions that are not fed

Note that in approximating the change in 
goal, all emission reductions that are not federally enforceable, but that were in the prp18b inventory, are acc

emission reductions at the Drake plant). This method of approximating the change in the haze index (given in the 2018 predicted reasonable progress goal at Canyonlands means of predicting the change to the reasonable progress goal, it Additional Analysis - PSAT Daily and Annual ContributionsThe following additional analysis is provided as additional weightSO2 and 4,000 tpy of NOx emissions because of The annual and daily PSAT impacts at Canyonlands are reviewed.As discussed earlier, Colorado’s rescaled sulfate provides the modeled PSAT sulfate concentrations (US (EUS), Mexico (MEX), Pacific Ocean (PO), and Outside Domain (OD) for the worst days. Colorado sulfatμg/m3 on an annual basis and decrease significantly in 

Figure 5: Annual PSAT in 2002 and 2018 

Figure 6 provides Colorado’s daily sulfate impact on daily sulfate impacts over 0.02 μg/m3 occur on multiplepoint sources. 

goal, all emission reductions that are not federally enforceable, but that were in the prp18b inventory, are acc

This method of approximating the change in the haze index (given i

at Canyonlands would only increase from 10.77 dv to 10.80 dv. 

means of predicting the change to the reasonable progress goal, it further supports a conclusion that the cha

PSAT Daily and Annual Contributions

The following additional analysis is provided as additional weight-of-evidence (WOE) that Colorado’s impact fSO2 and 4,000 tpy of NOx emissions because of lack of federal enforceability results in a negligible visibility iThe annual and daily PSAT impacts at Canyonlands are reviewed.

rescaled sulfate impact on Canyonlands is estimated at 3.17% on the worst 

concentrations (μg/m3) for each western State along with Canada (CAN)

US (EUS), Mexico (MEX), Pacific Ocean (PO), and Outside Domain (OD) for the worst days. Colorado sulfat

on an annual basis and decrease significantly in 2018 because of point source reductions. 

2002 and 2018 for Source Region Sulfate Impacts at Canyonlands

impact on Canyonlands in 2002 and 2018 on the worst days. As in

occur on multiple days throughout the year, particularly in July, and are 

goal, all emission reductions that are not federally enforceable, but that were in the prp18b inventory, are acc

This method of approximating the change in the haze index (given i

would only increase from 10.77 dv to 10.80 dv. 

a conclusion that the cha

evidence (WOE) that Colorado’s impact f

visibility i

orst 

) for each western State along with Canada (CAN)

US (EUS), Mexico (MEX), Pacific Ocean (PO), and Outside Domain (OD) for the worst days. Colorado sulfat

at Canyonlands on 

in 2002 and 2018 on the worst days. As in

days throughout the year, particularly in July, and are 
Figure 6: Daily PSAT in 2002 and 2018

Table 3 provides the daily 2018 sulfate contributions from Colorado. On several days Colorado contributes in μg/m3. Point sources are the largest contributor to sulfat

2002 and 2018 for Colorado Nitrate Impacts at Canyonlands on the W

daily 2018 sulfate contributions from Colorado. On several days Colorado contributes in 

are the largest contributor to sulfate on most days. 

on the W

daily 2018 sulfate contributions from Colorado. On several days Colorado contributes in 
Table 3: Daily PSAT in 2018 for Colorado Sulfate Impacts at Canyonlands on the Worst 

Class I 

Area Pollutant Date Source Region Model Scenario 

Nat. 

Fires & 

Bio. 

Anthro. 

Fires Mobile Area Point To

[ug/m3] [ug/m3] [ug/m3] [ug/m3] [ug/m3] [ug

CANY1 PS4 1/8/2018 CO base18b36k 0 0 0 0.001 0.006 0CANY1 PS4 4/17/2018 CO base18b36k 0 0 0 0 0 CANY1 PS4 5/8/2018 CO base18b36k 0 0 0 0 0 CANY1 PS4 5/20/2018 CO base18b36k 0.001 0 0 0 0.001 0CANY1 PS4 6/1/2018 CO base18b36k 0 0 0 0 0.001 0CANY1 PS4 6/22/2018 CO base18b36k 0 0 0 0 0 CANY1 PS4 6/28/2018 CO base18b36k 0 0 0 0.001 0.002 0CANY1 PS4 7/1/2018 CO base18b36k 0 0 0 0 0 CANY1 PS4 7/4/2018 CO base18b36k 0 0 0.001 0.002 0.012 0CANY1 PS4 7/7/2018 CO base18b36k 0 0 0.001 0.004 0.03 0CANY1 PS4 7/10/2018 CO base18b36k 0.001 0 0.004 0.011 0.097 0CANY1 PS4 7/13/2018 CO base18b36k 0.003 0 0.002 0.004 0.035 0CANY1 PS4 7/16/2018 CO base18b36k 0.004 0 0.001 0.003 0.03 0CANY1 PS4 7/22/2018 CO base18b36k 0 0 0.001 0.001 0.007 0CANY1 PS4 7/28/2018 CO base18b36k 0 0 0 0 0.001 0CANY1 PS4 8/9/2018 CO base18b36k 0 0 0 0 0.001 0CANY1 PS4 8/12/2018 CO base18b36k 0 0 0 0 0 CANY1 PS4 8/18/2018 CO base18b36k 0 0 0 0 0 CANY1 PS4 8/21/2018 CO base18b36k 0 0 0 0 0 CANY1 PS4 9/26/2018 CO base18b36k 0 0 0 0 0.002 0CANY1 PS4 11/1/2018 CO base18b36k 0 0.001 0.001 0.001 0.015 0CANY1 PS4 12/7/2018 CO base18b36k 0 0 0.001 0.002 0.02 0

Colorado’s rescaled nitrate impact on Canyonlands is estimated at 6.97% on the worst days in 2018. Figure 

PSAT nitrate concentrations (μg/m3) for each western State along with Canada (CAN), CENRAP (CEN), East

(MEX), Pacific Ocean (PO), and Outside Domain (OD) for the worst days. Colorado nitrate impacts are just a

annual basis and decrease slightly in 2018 because of mobile source reductions. 
Figure 7: Annual PSAT in 2002 and 2018 

Figure 8 provides Colorado’s daily nitrate impact on daily nitrate impacts over 0.02 μg/m3 occur in the summer and winter and primarily as the result of point, area

2002 and 2018 for Source Region Nitrate Impacts at Canyonlands

impact on Canyonlands in 2002 and 2018 on the worst days. As in

in the summer and winter and primarily as the result of point, area

on t

in 2002 and 2018 on the worst days. As in

in the summer and winter and primarily as the result of point, area
Figure 8: Daily PSAT in 2002 and 2018 

Table 4 provides the daily 2018 nitrate contributions from Colorado. There are multiple days identified on whgreater than 0.02 μg/m3. 

2002 and 2018 for Colorado Nitrate Impacts at Canyonlands on the W

daily 2018 nitrate contributions from Colorado. There are multiple days identified on whdaily 2018 nitrate contributions from Colorado. There are multiple days identified on wh
Table 4: Daily PSAT in 2018 for Colorado Nitrate Impacts at Canyonlands on the Worst 

Class I 

Area Pollutant Date Source Region Model Scenario 

Nat. 

Fires & 

Bio. 

Anthro. 

Fires Mobile Area Point To

[ug/m3] [ug/m3] [ug/m3] [ug/m3] [ug/m3] [ug

CANY1 PN3 1/8/2018 CO base18b36k 0.004 0 0.013 0.005 0.014 0.CANY1 PN3 4/17/2018 CO base18b36k 0 0 0 0 0 CANY1 PN3 5/8/2018 CO base18b36k 0 0 0 0 0 CANY1 PN3 5/20/2018 CO base18b36k 0 0 0 0 0 CANY1 PN3 6/1/2018 CO base18b36k 0 0 0 0 0 CANY1 PN3 6/22/2018 CO base18b36k 0 0 0 0 0 CANY1 PN3 6/28/2018 CO base18b36k 0.001 0 0.001 0.006 0.001 0.CANY1 PN3 7/1/2018 CO base18b36k 0 0 0 0 0 CANY1 PN3 7/4/2018 CO base18b36k 0.001 0 0 0.003 0.001 0.CANY1 PN3 7/7/2018 CO base18b36k 0.002 0 0.003 0.013 0.005 0.CANY1 PN3 7/10/2018 CO base18b36k 0 0 0.001 0 0.001 0.CANY1 PN3 7/13/2018 CO base18b36k 0 0 0 0 0 CANY1 PN3 7/16/2018 CO base18b36k 0 0 0 0 0 CANY1 PN3 7/22/2018 CO base18b36k 0 0 0 0 0 CANY1 PN3 7/28/2018 CO base18b36k 0 0 0 0 0 CANY1 PN3 8/9/2018 CO base18b36k 0 0 0 0 0 CANY1 PN3 8/12/2018 CO base18b36k 0 0 0 0 0 CANY1 PN3 8/18/2018 CO base18b36k 0 0 0 0 0 CANY1 PN3 8/21/2018 CO base18b36k 0 0 0 0 0 CANY1 PN3 9/26/2018 CO base18b36k 0.002 0 0.002 0.003 0.001 0.CANY1 PN3 11/1/2018 CO base18b36k 0.006 0.001 0.013 0.031 0.026 0.CANY1 PN3 12/7/2018 CO base18b36k 0.004 0 0.013 0.039 0.019 0.

WEP Evaluation of Colorado Impacts on nearby Class I areas:

The following WEP analysis is provided as additional weight-of-evidence (WOE) that Colorado’s sulfate and n

Canyonlands. As indicated in Figure 9, the dominant grid cells that contribute to air parcels arriving in Canyo

Arizona. Figure 10 below, provides the SOx WEP for Canyonlands. As shown, none of the 36-km grid cells 

more than 10% on a normalized scale. Similarly, Figure 11 below provides the NOx WEP for Canyonlands. grid cells in Colorado contribute more than 10% on a normalized scale. 
The WEP analysis results further support a conclusion that Colorado does not interfere with the ability of nea

reasonable progress goals. 

Figure 9: Canyonlands 5-Year Meteorology (2000-2004) Back-Trajectories for the Wors
Figure 10: Canyonlands SOx Weighted Emissions Potential for the 2018 Worst Day
Figure 11: Canyonlands NOx Weighted Emissions Potential for the 2018 Worst Day
Review of Current and Future Year Inventories

In Colorado, Regulation Number 3 (Stationary Source Permitting) requires any non-exempt stationary source 

(uncontrolled actual emissions in a non-attainment area) or 2 ton/year (uncontrolled actual emissions in an atarea) of criteria pollutant emissions to file an Air Pollutant Emissions Notice (APEN) with the Division. Thus, 

emission threshold is very low relative to most western states and any stationary sources below the APEN tharea sources. The PSAT modeling incorporated a present and future emission inventory (Plan 2002c and Base 2018b) that 

categories (see Table 5). These 12 categories were mapped into five categories in the PSAT model: point, a

fires/biogenic, and anthropogenic fires. The emission inventories show a net decrease of 32,799.2 tpy of SO

NOx between 2002 (Plan 2002c) and 2018 (Base 2018b) before the implementation of any anticipated BART 

controls. 

Table 5: Colorado Emission Inventories used in PSAT modeling (Plan 2002c and Base 2

The Base 2018b emission inventory (EI) contains about 3,350 tpy of surplus SO2 in the Colorado point sourc

with two future power plants that have been removed from the latest PRP 2018b emission inventory. Thus, a

(see the above PSAT analysis - Figure 2) produces a slightly conservative estimate of a 0.87% increase in su

Region Scenario Year Point [tpy] Anthro Fire [tpy] Natural Fire [tpy] Biogenic [tpy] Area [tpy] WRAP Area O&G [tpy] Off-Shore [tpy] On-Road Mobile [tpy] Off-Road Mobile [tpy] Road Dust [tpy] 

CO Plan02c 2002 97016.4 107.6 3334.9 - 6504.4 259.7 - 4389.2 3014.9 4.1 

CO Base18b 2018 69262.5 91.4 3334.9 - 7676.1 8.5 - 676.6 780.7 0.0 

Delta (27753.9) (16.3) 0.0 - 1171.7 (251.2) - (3712.6) (2234.3) (4.1) 

Reduction Percentage: -28.6% -15.1% 0.0% - 18.0% -96.7% - -84.6% -74.1% -100.0% 

Source C ategory % of Total: 84.6% 0.1% 4.1% - 9.4% 0.0% - 0.8% 1.0% 0.0% 

Region Scenario Year Point [tpy] Anthro Fire [tpy] Natural Fire [tpy] Biogenic [tpy] Area [tpy] WRAP Area O&G [tpy] Off-Shore [tpy] On-Road Mobile [tpy] Off-Road Mobile [tpy] Road Dust [tpy] 

CO Plan02c 2002 117868.9 519.9 9377.1 37348.8 11645.1 23350.9 - 141883.5 62447.2 0.9 

CO Base18b 2018 112241.2 408.5 9377.1 37348.8 16360.3 27992.9 - 45249.1 40803.9 0.0 

Delta (5627.7) (111.4) 0.0 0.0 4715.2 4642.0 - (96634.4) (21643.3) (0.9) 

Reduction Percentage: -4.8% -21.4% 0.0% 0.0% 40.5% 19.9% - -68.1% -34.7% -100.0% 

Source C ategory % of Total: 38.7% 0.1% 3.2% 12.9% 5.6% 9.7% - 15.6% 14.1% 0.0% 

Sulfur Dioxide (gas and particulates) Nitrogen oxides (gas and particulates)
Similarly, the Base 2018b emission inventory (EI) contains about 3,350 tpy of surplus NOx increases in the C

emissions associated with the two future power plants that have been removed from the latest PRP 2018b em

Base 2018b EI also includes 4,000 tpy of Colorado mobile source NOx reductions that may not be federally edetermine from the EI) and therefore these NOx reductions are added back into the Base 2018b EI. The net 

the apparent surplus and restored increase is 650 tpy (+4,000 - 3,350 = +650). Thus, adding 4,000 tpy of NO

PSAT analysis - Figure 3) produces a very conservative estimate of a 0.09% increase in nitrate extinction. Colorado point source baseline emissions were estimated by using reported APEN emission data for 2002 thEconomic Growth Analysis System (EGAS) model to forecast future emissions in 2018. Since electric generarepresent a large portion of SO2 and NOx emissions, the WRAP used projected 2018 power demand from thInformation Administration (EIA) to estimate the number of future power plants across the west. In Colorado, 

inventory included two additional 500 MW power plants and the newly constructed 750 MW Comanche Unit 3 

below – highlighted in orange). The SO2 and NOx emissions for the other power plants were based on the 2

grown to 2018 based on utilization factors along with consideration of any future emission controls. The SO2 and NOx emission reductions associated with BART were included in the latest PRP 2018b emissio

indicated in Tables 4 and 5, respectively (new Comanche Unit 3 is highlighted in orange). The shutdown of Aanticipated by 2018, so no emissions from these two sources are included in the total. The two future power 

the PRP 2018b emission inventory because of decreased projections of annual electricity demand, as well de

renewable energy portfolio standards in Colorado. Together these have diminished the need for an additionacapacity in 2018. Based on a review of the current and future emission inventory information, it can be concluded that nearby S

on the Colorado measures that are not yet federally enforceable in order to meet their reasonable progress g
Table 6: Significant Coal-Fired Boilers included in the Plan 2002c/Base 2018b/PRP 2018b Point Source E

Inventories 
Table 7: Significant Coal-Fired Boilers included in the Plan 2002c/Base 2018b/PRP 2018b Point Source N

Inventories